Bugs, Cicadas, Aphids, and Scale-insects 185 



it was found that at Washington four full generations are regularly developed, 

 with the possibility of a partial fifth generation. On a number of potted 

 trees a single overwintered female was left to each tree. After the full 

 progeny of this individual had gone out over the tree all were removed 

 again, except one of the oldest and fertilized females. This method was 

 continued for each generation throughout the breeding season. Some 

 interesting records . . . were thus obtained, which indicate the fecundity 

 of the females as well as the number of generations." 



From these records it may be fairly estimated that an average of 200 

 females (in addition to about as many males) are produced by each female, 

 and that there are four generations each year in the latitude of Washington, 

 D. C. Thus the product of a single overwintered female in a single year 

 amounts to 3,216,080,400 male and female descendants. This total is, 

 of course, never reached, because only a part of each generation reaches 

 maturity and produces young, but in a favorable season on a tree newly 

 infested (and thus providing a plentiful food-supply) a large majority of 

 each generation do most probably go through their normal existence. 

 "Neither the rapidity with which trees become infested," add Howard and 

 Marlatt, "nor the fatal effect which so early follows the appearance of this 

 scale-insect is therefore to be wondered at." 



But not all scale-insects are so specialized either structurally or physio- 

 logically as the pernicious (or San Jose) scale. The females of some species 

 retain the eyes, antennae, and legs through their whole life and can crawl 

 about if need be at any time. Others show a sort of transition between 

 these two extremes of activity and quiescence, having the legs present, but 

 in adult life much reduced in size and probably functionless, or at best 

 capable of carrying the insect but feebly and briefly. In the matter of the 

 covering, too, there is much variety; some scales secrete no wax at all, but 

 have the body-wall of the back specially thickened and made firm so as 

 to act as an effective covering-shield underneath which, somewhat as with 

 a turtle, the legs and head can be concealed. Others secrete filaments or 

 tufts of soft white wax which form a sort of felted protecting covering for the 

 body. In a general way the various scale-insects may be instructively 

 gathered into three groups, depending on the characters of the females; 

 in the first group the females retain the antennae, eyes, and legs, and the 

 segmented condition of the body (typical of normal insects) and are capable 

 of locomotion throughout life; they secrete wax usually in the shape of white 

 cottony filaments or masses with which they cover the body more or less 

 completely, sometimes forming conspicuous waxen egg-sacs at the posterior 

 extremity of the body; the females of the second group retain their legs 

 and antennae through life, but have them in reduced condition when adult, 

 and although capable of feeble motion, usually lie quiescent; they commonly 



